There are a few ways you can gain faith points in Stronghold Kingdoms:
Faith points are a reward for completing many quests and you can gain hundreds of thousands of them this way. But some quests take 100,000 faith points to complete such as the last inquisition quest so in essence the cost versus reward probably level themselves out. You can skip some of the quests if you feel you need the faith points badly for other things.
The quest wheel can reward you with up to 30,000 faith points at the wheels highest level. Because you gain a lot of wheel tokens from quests you will usually hit a few faith point rewards on the wheel. But my advice is to keep all your wheel tokens until you reach duke, that way you can spin all your tokens on the level 5 quest wheel, and gain the largest rewards.
Level 16 theology research gives you 120 faith points per day. It’s actually quite a small amount but over time it all builds up.
Religious Buildings in your Village
Placing a cathedral, churches and other religious buildings in your village give you a large amount of faith points per day. The bigger buildings like the cathedral cost a lot of gold to place and if you really want to build up a lot of faith points place all the religious buildings near the start of building your new villages.
At level 10 parish churches give you 60 faith points per day per village. This can build up to a very large boost per day because the more villages you have the more faith points you gain. So if you have 10 villages you can gain an extra 600 faith points per day if the churches are all at max level in your parishes.